A pro-democracy activist who threw a tuna sandwich at Leung Chun-ying, but missed the former Hong Kong leader and hit a policeman instead, was on Tuesday convicted and jailed for three weeks.

Avery Ng Man-yuen, 40, was found guilty of one count of common assault over a hurled sandwich that hit police officer Lau Wing-kwan on September 4 last year.

The West Kowloon Court heard that the League of Social Democrats chairman bought two sandwiches while he was on his way to a polling station in Central for the Legislative Council elections. One snack was for his breakfast, but the other was a reminder for Leung that the elderly were struggling to even afford such a meal, he said.

Ng then testified that it was Leung’s “very smug” expression that invited him to “bring it on” and lob the pungent snack.

But magistrate So Wai-tak found that Ng was only making up excuses to rationalise his behaviour after he intentionally launched the attack to express his dissatisfaction with the government. So concluded the activist was an unreliable witness.

Ng said during his mitigation that he did not mind a heavy punishment. “I am deeply honoured to be able to do something for the underprivileged,” he told the magistrate. “I hope you understand that no deterrent sentence will work on me.”